Your Federal Quarterly Tax Payments are due April 15th

# INFILTRATION by 8VG6j46

VIEWS: 26 PAGES: 36

• pg 1
```									INFILTRATION

AE 520

1
Infiltration Lesson
Objectives
• Understand the factors affecting soil
water infiltration
• Be able to estimate infiltration rate
using the Horton Equation and the
Green-Ampt Equation
• Understand the advantages of the
various infiltration functions.

2
INFILTRATE
To cause (as a liquid) to permeate
something by penetrating its pores or
interstices.

Webster’s Ninth New Collegiate
Dictionary

3
INFILTRATION
• The movement of water through the
soil surface into the soil profile.
• After Precipitation, it is the most
important process controlling the
water balance on a field.
• Expressed as total depth or as a
velocity called the infiltration rate

4
Infiltration may be
controlled by 3 types of
factors
• Supply Factors

• Surface Factors

• Profile Factors

5
Infiltration Control Supply
Factors
• The water supply for infiltration may
be:
• Rainfall
• Surface Pond Storage
• Irrigation
• Infiltration Rate will be the minimum
of supply and Capacity
6
Infiltration Control Surface
Factors
• Degree of Surface Crusting
– Clay content of the surface
– Effect of drop impact
• Degree of Surface Porosity
– Soil texture
– Soil Structure
– Vegetation Cover
– Inwash of fine particles
– Cracks and other macropores
7
EFFECT OF PROTECTIVE
COVER ON INFILTRATION

8
Infiltration Control Profile
Factors
• Hydraulic Conductivity of the soil
layers
• Moisture Content of the soil layers
near the surface.
• Rate of internal drainage

9
Measurement of Infiltration
Sprinkler Infiltrometer
Rainfall

Runoff

Infiltration

Infiltration = Rainfall - Runoff

10
Infiltration with supply
control

Supply rate
Rate
fc

Time
11
Measurement of Infiltration
Ring Infiltrometer

12
Infiltration with Soil Control
DEPTH (F)

TIME           13
Infiltration with Soil Control
fo
INFILTRATION

DEPTH / TIME

dF
RATE (f)

f
dT

fc
TIME        14
Field Surface
Yp + Ym
During
Infiltration      YT

Static
Z
Soil
Profile

Water Table
-   0    +
POTENTIAL
Kostiakov’s Equation

F = CTn f = CnTn-1

n

1

C

log T             16
Horton’s Equation
f  fc + f0  fc e    Kt

Log(f0 - fc )
Log(f-fc)

1
K

t
17
Darcy’s Equation

dY           dY
v K       q  KA
dz           dz

18
SOIL MOISTURE CONTENT
0
DEPTH FROM INFILTRATION       ZONE OF SATURATION

TRANSITION   ZONE
SURFACE

TRANSMISSION
ZONE

WETTING
ZONE

WETTING FRONT

19
HOLTAN’S CONCEPT OF

ACCUMULATED INFILTRATION DEPTH
INFILTRATION

TIME          20
Holtan’s Equation
P
S F 
f  fc + A     
 S 

P
1
A
1
log ((S-F)/S)      21
Green-Ampt Equation
KDQDY
f K+
F

KDQDY
f
1

K

1/F               22
Green-Ampt Infiltration
Equation
1                   Soil Surface
Yp = 0       K = Constant
Yz = 0       Q  Q f= constant
Wet        Lf
Ym = Yf
Wetting Front
2        Yp = 0       Q  Qi = constant
Dry             Yz = Lf
Ym = Yi

23
Green-Ampt Infiltration
Equation
dY  0  L f + Yi  0  0  Yf
 L f + Yi  Yf
FromtheDarcyEquation

V  K
dY
 K
 L f + Yi  Yf 
dL              Lf
24
Green-Ampt Infiltration
Equation
• Both Yi and Yf are negative and Yi <
Yf . Therefore DY < 0 and the
negative signs cancel.

 DY + L f      DY 
V  K            K    + 1
 Lf            Lf    
25
Green-Ampt Infiltration
Equation
•   Total Depth of Infiltration = F
•   F = Lf(Qf  Qi) = LfDQ
•   Lf = F/DQ
•   assuming the velocity V = the
infiltration rate f
     DQDY      KDQDY      B
f  K 1 +       K+        A+
       F         F        F
26
Green-Ampt Computations

     D YD Q     B
f  K 1 +        A+
       F        F
whe re A  K
and B  KD YD Q
27
Infiltration Rate at the
Beginning of a Time
Increment

B
f1  A +
F1

28
Infiltration Rate at the
Beginning of a Time
Increment

B
f2  A +
F2

29
Average Infiltration Rate
over a Time Period
DF   f 1 + f2

DT       2
Rearranging:
DF   f1 + f2
-         0
DT      2
30
Upper Limit on the
Infiltration During the Period

F2  F1 1   B      B
 A + + A +   0
DT     2  F1     F2 
F2   F1      B   B
         A    
DT DT        2F1 2F2

31
Multiplying by F2 and
Rearranging

1 2           B   F1      B
F2  ( A +    +    )F2   0
DT            2F1 DT       2
F1 will always be known or assumed.
Therefore F2 is the only unknown,
and the function is a quadratic.
32
for F2
 b  b  4ac
2
F2 
2a
1                 B
a=                c 
DT                  2
B   F1        c
b  A           A +  aF1
2F1 DT         F1
33
for F2
equation applies.
• The actual value of F2 can not exceed
F1 + Supply during the period. At the
end of each time step, this limit must
be checked, and if the GA equation
gives a larger value, then the supply
will be limiting.
34
Green-Ampt Infiltration
K = 2 mm/hr, D T = 0.25 hr, DQ = 0.1 cc/cc, DY = 5000 mm
Total Rainfall = 114 mm, Total Runoff = 37.26 mm
35.0

30.0

25.0
Depth in mm

Rainfall

20.0                                                              Infilt

Runoff

15.0

10.0

5.0

0.0
0.00     0.50     1.00      1.50     2.00     2.50      3.00            3.50
Time in Hours

35
Green-Ampt Infiltration
K = 2 mm/hr, DT = 0.25 hr, DQ= 0.1cc/cc, DY = 5000 mm
Total Rainfall = 114 mm, Total Runoff = 53.15 mm
35

30
Depth in Millimeters

25
Rainfall

20                                                           Infilt

Runoff
15

10

5

0
0.00   0.50     1.00      1.50     2.00     2.50     3.00            3.50
Time in Hours

36

```
To top